Thermal inkjet printers typically utilize a printhead that includes an array of orifices (also called nozzles) through which ink is ejected on to paper or other print media. Ink filled channels feed ink to a firing chamber at each orifice from a reservoir ink source. Applied individually to addressable thermal elements, such as resistors, ink within a firing chamber is heated, causing the ink to bubble and thus expel ink from the chamber out through the orifice. As ink is expelled, the bubble collapses and more ink fills the chamber through the channels from the reservoir, allowing for repetition of the ink expulsion sequence.
Many conventional thermal inkjet printheads are currently produced with ink feed channels formed in a semiconductor substrate structure that includes the firing resistors. A barrier layer is formed on the substrate structure and a metal or polyimide orifice plate is attached to the barrier layer. The ink feed channels extend lengthwise along the printhead to carry ink to openings in the barrier layer that direct ink to the resistors. The barrier layer material is often a thick, organic photosensitive material laminated onto the substrate structure, and then patterned and etched with the desired opening and chamber configuration.
The firing resistors are formed in thin film layers in the substrate structure. The barrier layer and orifice plate in conventional printheads are not suitable for circuit integration. Thus, the control and drive circuits enabling the resistors and the conductive traces to bonding pads that provide external electrical connections to the printhead must be laid out along the length of the substrate structure between ink channels in the thin film layers of the substrate structure. Such “two dimensional” configurations take up significant space on the substrate die and present special challenges for efficiently routing conductive traces between the bond pads and the control and drive circuit elements. Also, during printing operations, ink is ejected in a direction perpendicular to the surface of the substrate structure. Again, because the barrier layer and orifice plate in conventional printheads are not suitable for circuit integration, there is no easy way to detect or influence the ink drops in the direction of drop ejection.
The structures shown in the figures, which are not to scale, are presented in an illustrative manner to help show pertinent structural and processing features for example embodiments of the disclosure. Due to space limitations and for clarity, in some instances where a structural feature or element occurs multiple times in a figure, fewer than all of the multiple occurrences are indicated by the corresponding part number.